1. Field of the Invention
The invention pertains to the field of valve event reduction. More particularly, the invention pertains to valve event reduction through operation of a fast-acting cam phaser.
2. Description of Related Art
For engines with a fixed geometry camshaft actuated inlet and exhaust valves, a variable cam timing (VCT) phaser is useful for improving engine operation. Since most VCT phasers are relatively slow acting devices, they can advance or retard the camshaft, but to change between the positions, will take numerous engine cycles to accomplish, even at engine cranking speeds.
To vary the valve event or more specifically, shorten the effective intake or exhaust valve event, numerous methods have been implemented in the prior art, for example U.S. Pat. No. 5,297,507 discloses a method of reducing the valve event by varying the angular velocity of the camshaft. A variable event timing mechanism has a flexible lost motion coupling (valve spring) interposed between the drive wheel and the camshaft. For the camshaft to open normally and close early, the camshaft rotates at substantially the same speed as the drive wheel during opening and closing of the valve. The camshaft is accelerated by the valve spring to lead the drive wheel and thereby reduce the duration of the valve event. For the camshaft to open late and close normally, the camshaft is retarded by the valve spring to lag behind the drive wheel, and during closing of the valve, the camshaft rotates at substantially the same speed as the drive wheel, thereby reducing the duration of the valve event.
U.S. Pat. No. 6,405,694 discloses an exhaust valve advanced-closing control for controlling the valve closing timing of the exhaust valve to the advance side without using valve overlap of a valve timing control means. In a second embodiment, a changeover may be made between the exhaust valve advanced-closing control for controlling the timing to close the exhaust valve to the advance side of the intake TDC and the retarded exhaust valve closing control for controlling the timing to close the exhaust valve to the retard side of the TDC.
US 2003/0121484A1 discloses a method of altering the continuously variable valve timing, lift, and duration by altering the location of the pivot of a rocker arm. The overlap and valve lift duration increases when the valve lift increases. The chain timing, lift and duration are continuous and a function of engine speed.
SAE Technical Paper No. 930825 discloses a variable event timing system that varies both the event length and phasing to optimize the breathing cycle of the engine. A drive shaft replaces an existing camshaft and uses the original drive flange configuration to drive each of the camshafts via a peg that engages with a drive slot in each of the camshafts. The drive shaft transmits torque and runs in its own bearing housings that are moved offset from the drive centerline relative to the camshaft centerline. By applying the offset drive shaft to drive the camshafts, the force applied is of a variable velocity, which accelerates and decelerates the individual camshafts during a single cam revolution. By adjusting the relationship of the drive shaft and the camshaft, the valves open late and close early, shortening the intake valve duration.